Trick playback modes are achieved with conventional digital storage media by dividing the content into sectors of a specific size and then using an address table containing sector addresses and index numbers, time codes, content titles, and content encoding unit information.
FIG. 22 describes how a trick playback mode is implemented with conventional digital storage media. FIG. 22 (a) shows the data recording structure, and (b) to (f) are various sector address lookup tables recorded with the data in order to achieve a trick playback mode. More specifically, tables (b) to (f) cross reference index numbers, time codes, content titles, sequence header numbers (indicating the start of each sequence, that is, the content encoding unit), and the first and last sector address of each I-picture (a picture encoding type). The content is data compressed in sequential units using MPEG-1 or other compression encoding technique, then segmented into sector units of a specific size for recording to optical disc. A unique sector address is assigned to each sector. The sectors are further divided into blocks. Each block starts with a header containing a synchronization signal, common sector address, unique block address, and a parity bit, the header is followed by the content data; and the block then ends with an ECC parity word for error correction.
Trick playback modes are achieved with multimedia content recorded in this manner as follows.
It should be noted that playback of compressed content cannot start from any desired location. More specifically, playback can only start from specific positions, that is, the sequence header. This means that in order to randomly access content when the user selects an access point such as the beginning of a song, the sector address at the start of the selected content is first determined from table (d) in FIG. 22. Playback then starts from the sector address found in table (e) for the sector containing the sequence header containing the address closest to the sector address found in table (d).
If playback positions are defined more precisely, the user can use the index numbers to specify where in a song (for example) to start playback. In this case the sector address corresponding to the specified index number is found from table (b) to start playback. If the user specifies the playback start position using a time code, the sector address closest to the specified time code is found from table (c), and playback starts from the sector address found in table (e) of the sector containing the sequence header with an address closest to the sector address found in table (c). Fast-forward and fast-reverse play modes are similarly achieved by sequentially finding the start and end sector addresses of the independently reproducible I-pictures from table (f) and then skipping from I-picture to I-picture to play only the I-pictures in the forward or reverse play direction. The methods described above are known, for example, from U.S. Pat. No. 6,002,834, Optical Disk Having Table Relating Sector Address and Time and Optical Disk Reproducing Apparatus.
As will be understood from the tables in FIG. 22, the index numbers, time codes, sequence headers, and I-pictures are managed using sequential numbers in the prior art method described above. This means that in order to start playback from 10 seconds into content B, for example, this relative time must be converted to a specific value in the continuous time code. Because the total playback time of content A is unknown, however, an accurate time code for starting playback from 10 seconds into content B cannot be determined.
A further problem arises from the indeterminate length of the I-pictures. More specifically, because the I-picture length is variable, it is not known how much data must be read in order to skip to the next I-picture in fast-forward and fast-reverse play modes.